Automatic transmission

ABSTRACT

An automatic transmission includes a first rotating element provided by coupling a sun gear of a second planetary gear set and a carrier of a third planetary gear set to each other, a second rotating element provided by coupling a carrier of the second planetary gear set and a ring gear of the third planetary gear set to each other, a third rotating element provided by a ring gear of the second planetary gear set, and a fourth rotating element provided by a sun gear of the third planetary gear set. The first rotating element and the second rotating element are coupled to a case by first and second brakes, the fourth and first rotating elements are coupled to a ring gear of a first planetary gear set via first and second clutches, the second and first rotating elements are coupled to an input shaft via third and fourth clutches, and the third rotating element is integrally coupled to an output gear, so that the automatic transmission can provide eight forward gear stages by changing a combination of two of the clutches and brakes which are engaged to each other.

INCORPORATION BY REFERENCE

[0001] The disclosure of Japanese Patent Application No. 2001-332177filed on Oct. 30, 2001, including the specification, drawings andabstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of Invention

[0003] The invention relates to an automatic transmission, and moreparticularly to an automatic transmission capable of providing seven ormore forward gear stages or speeds by using three planetary gear setsand also capable of shifting from one gear stage to another gear stageby changing a combination of two different engaging elements, such asclutches and brakes, to be engaged.

[0004] 2. Description of Related Art

[0005] Automatic transmissions of motor vehicles, each including aplurality of planetary gear sets, clutches and brakes, have been widelyused. Japanese Laid-Open Patent Publication No. 2000-266138(JP-A-2000-266138) discloses an example of such an automatictransmission which is able to provide seven forward gear stages by usingfour planetary gear sets. Also, Japanese Laid-Open Patent PublicationNo. 2001-82555 (JP-A-2001-82555) discloses another example of theautomatic transmission which is able to provide ten forward gear stagesby using three planetary gear sets.

[0006] The automatic transmission as disclosed in JP-A-2000-266138,which uses four planetary gear sets, has a relatively large axiallength, and may suffer from a difficulty in installing the transmissionon the vehicle, an increased weight, and an increased manufacturingcost. On the other hand, the automatic transmission as disclosed inJP-A-2001-82555 can be comparatively easily installed on the vehicle.However, there is a need to change a combination of the maximum of fourengaging elements (clutches and/or brakes) to be engaged so as to shiftthe transmission from one speed to another speed. Thus, the automatictransmission requires complicated, high-accuracy shift control, and maysuffer from shift shocks.

SUMMARY OF THE INVENTION

[0007] In view of the above situation, the invention has been made toprovide an automatic transmission constructed as described below.

[0008] An automatic transmission according to one aspect of theinvention includes (a) a first transmitting portion including an inputmember that is rotated at reduced speed to output power from anintermediate output member, and (b) a second transmitting portionincluding a second planetary gear set and a third planetary gear seteach of which includes a sun gear, a carrier and a ring gear, at leastone of the sun gear, the carrier and the ring gear of the secondplanetary gear set being coupled to at least one of the sun gear, thecarrier and the ring gear of the third planetary gear set to provide afirst rotating element, a second rotating element, a third rotatingelement and a fourth rotating element, which are arranged in the orderof description from one end to the other end in a nomogram in whichspeeds of rotation of the first, second, third and fourth rotatingelements are represented by straight lines. The second transmittingportion further includes a first brake that selectively stops rotationof the first rotating element, a second brake that selectively stopsrotation of the second rotating element, a first clutch that selectivelycouples the fourth rotating element to the intermediate output member, asecond clutch that selectively couples the first rotating element to theintermediate output member, a third clutch that selectively couples thesecond rotating element to the input member, and a fourth clutch thatselectively couples the first rotating elements to the input member, thethird rotating element being integrally coupled to an output member tooutput rotary power. In the automatic transmission thus constructed, afirst-speed gear stage having the largest gear ratio is established whenthe first clutch and the second brake are engaged, a second-speed gearstage having a smaller gear ratio than that of the first-speed gearstage is established when the first clutch and the first brake areengaged, a third-speed gear stage having a smaller gear ratio than thatof the second-speed gear stage is established when the first clutch andthe second clutch are engaged, and a fourth-speed gear stage having asmaller gear ratio than that of the third-speed gear stage isestablished when the first clutch and the fourth clutch are engaged, afifth-speed gear stage having a smaller gear ratio than that of thefourth-speed gear stage is established when the first clutch and thethird clutch are engaged, a sixth-speed gear stage having a smaller gearratio than that of the fifth-speed gear stage is established when thethird clutch and the fourth clutch are engaged, a seventh-speed gearstage having a smaller gear ratio than that of the sixth-speed gearstage is established when the second clutch and the third clutch areengaged, an eighth-speed gear stage having a smaller gear ratio thanthat of the seventh-speed gear stage is established when the thirdclutch and the first brake are engaged.

[0009] The gear ratio as mentioned above means the ratio of the speed ofrotation of the input member to the speed of rotation of the outputmember (=rotation speed of input member/rotation speed of outputmember).

[0010] With the automatic transmission constructed as described above,the eight forward speeds are provided by the first transmitting portion,the second transmitting portion mainly including two planetary gearsets, four clutches and two brakes. Thus, the automatic transmission ismade light-weight and compact, as compared with the case where fourplanetary gear sets are used. Furthermore, since shifting from one speedto another speed is effected only by changing the combination of twoengaging elements (clutches and/or brakes), shift control can be easilyperformed, and shift shocks are advantageously reduced.

[0011] According to another aspect of the invention, there is providedan automatic transmission which includes (a) a first transmittingportion including an input member that is rotated at reduced speed tooutput power from an intermediate output member, and (b) a secondtransmitting portion including a second planetary gear set and a thirdplanetary gear set each of which includes a sun gear, a carrier and aring gear, at least one of the sun gear, the carrier and the ring gearof the second planetary gear set being coupled to at least one of thesun gear, the carrier and the ring gear of the third planetary gear setto provide a first rotating element, a second rotating element, a thirdrotating element and a fourth rotating element, which are arranged inthe order of description from one end to the other end in a nomogram inwhich speeds of rotation of the first, second, third and fourth rotatingelements are represented by straight lines. The second transmittingportion further includes a first brake that selectively stops rotationof the first rotating element, a second brake that selectively stopsrotation of the second rotating element, a first clutch that selectivelycouples the fourth rotating element to the intermediate output member, asecond clutch that selectively couples the first rotating element to theintermediate output member, a third clutch that selectively couples thesecond rotating element to the input member, and a fourth clutch thatselectively couples the first rotating elements to the input member, thethird rotating element being integrally coupled to an output member tooutput rotary power. In the automatic transmission thus constructed, afirst-speed gear stage having the largest gear ratio is established whenthe first clutch and the second brake are engaged, a second-speed gearstage having a smaller gear ratio than that of the first-speed gearstage is established when the first clutch and the first brake areengaged, a third-speed gear stage having a smaller gear ratio than thatof the second-speed gear stage is established when the first clutch andthe second clutch are engaged, and a fourth-speed gear stage having asmaller gear ratio than that of the third-speed gear stage isestablished when the first clutch and the fourth clutch are engaged, afifth-speed gear stage having a smaller gear ratio than that of thefourth-speed gear stage is established when the third clutch and thefourth clutch are engaged, a sixth-speed gear stage having a smallergear ratio than that of the fifth-speed gear stage is established whenthe second clutch and the third clutch are engaged, a seventh-speed gearstage having a smaller gear ratio than that of the sixth-speed gearstage is established when the third clutch and the first brake areengaged.

[0012] With the automatic transmission constructed as described above,the seven forward speeds are provided by the first transmitting portion,the second transmitting portion mainly including two planetary gearsets, four clutches and two brakes. Thus, the automatic transmission ismade light-weight and compact, as compared with the case where fourplanetary gear sets are used. Furthermore, since shifting from one speedto another speed is effected only by changing the combination of twoengaging elements (clutches and/or brakes), shift control can be easilyperformed, and shift shocks are advantageously reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above-mentioned exemplary embodiment and other exemplaryembodiments, objects, features, advantages, technical and industrialsignificance of this invention will be better understood by reading thefollowing detailed description of the exemplary embodiments of theinvention, when considered in connection with the accompanying drawings,in which:

[0014]FIG. 1a is a schematic view showing an automatic transmission of amotor vehicle according to a first embodiment of the invention;

[0015]FIG. 1b is an operation table according to which each gear stageof the automatic transmission of the first embodiment as shown in FIG.1a is established;

[0016]FIG. 2 is a nomogram plotted with respect to the automatictransmission of the first embodiment of the invention;

[0017]FIG. 3 is a schematic view showing a modified example of theautomatic transmission of a motor vehicle according to the firstembodiment of the invention;

[0018]FIG. 4a is a schematic view showing an automatic transmission of amotor vehicle according to a second embodiment of the invention;

[0019]FIG. 4b is an operation table according to which each gear stageof the automatic transmission of the second embodiment is established;

[0020]FIG. 5 is a nomogram plotted with respect to the automatictransmission of the second embodiment;

[0021]FIG. 6 is a schematic view showing a modified example of theautomatic transmission of a motor vehicle according to the secondembodiment of the invention;

[0022]FIG. 7a is a schematic view showing an automatic transmission of amotor vehicle according to a third embodiment of the invention;

[0023]FIG. 7b is an operation table according to which each gear stageof the automatic transmission of the third embodiment is established;

[0024]FIG. 8 is a nomogram plotted with respect to the automatictransmission of the third embodiment;

[0025]FIG. 9 is a schematic view showing a modified example of theautomatic transmission of a motor vehicle according to the thirdembodiment of the invention;

[0026]FIG. 10a is a schematic view showing an automatic transmission ofa motor vehicle according to a fourth embodiment of the invention;

[0027]FIG. 10b is an operation table according to which each gear stageof the automatic transmission of the fourth embodiment is established;

[0028]FIG. 11 is a nomogram plotted with respect to the automatictransmission of the fourth embodiment;

[0029]FIG. 12 is a schematic view showing a modified example of theautomatic transmission of a motor vehicle according to the fourthembodiment of the invention;

[0030]FIG. 13a is a schematic view showing an automatic transmission ofa motor vehicle according to a fifth embodiment of the invention;

[0031]FIG. 13b is an operation table according to which each gear stageof the automatic transmission of the fifth embodiment is established;

[0032]FIG. 14 is a nomogram plotted with respect to the automatictransmission of the fifth embodiment;

[0033]FIG. 15 is a schematic view showing a modified example of theautomatic transmission of a motor vehicle according to the fifthembodiment of the invention;

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0034] In the following description and the accompanying drawings, theinvention will be described in more detail with reference to exemplaryembodiments.

[0035] The invention is preferably applied to an automatic transmissionof a motor vehicle, which receives rotary power from a driving powersource, such as an internal combustion engine, via a fluid coupling suchas a torque converter, changes the speed of rotation at a given gearratio, and transmits the power from an output member, such as an outputgear or an output shaft, to right and left driving wheels, via adifferential gear unit. An input member of the transmission may be aturbine shaft of the torque converter. It is to be understood that theinvention may also be applied to automatic transmissions for use insystems other than motor vehicles.

[0036] The automatic transmission may be transversely or laterallyinstalled on, for example, a front engine front drive (FF) vehicle, suchthat the axis of the transmission extends in the width direction of thevehicle, or may be longitudinally installed on, for example, a frontengine rear drive (FR) vehicle, such that the axis of the transmissionextends in the longitudinal or running direction of the vehicle.

[0037] The automatic transmission may automatically change its gearratio depending upon vehicle operating conditions, such as anaccelerator pedal position and a vehicle speed, or may change its gearratio in accordance with manual shifting operations (e.g., upshiftingand downshifting operations) by the vehicle operator. The automatictransmission according to exemplary embodiments of the invention is ableto establish seven or eight forward gear stages, and also establish areverse gear stage by engaging a second clutch and a second brake (whichwill be described later) provided in the automatic transmission and ahigh-speed reverse gear having a small gear ratio by engaging a forthclutch (which will be described later) and the second brake.

[0038] The first through fourth clutches and the first and second brakesas described later may preferably be in the form of hydraulicallyoperated friction devices of, for example, multiple-disc type,single-disc type or belt type, which are frictionally engaged by meansof hydraulic cylinders. Other coupling devices, such as those ofelectromagnetic type, may also be used as the clutches and brakes. Aone-way clutch or clutches may also be provided in parallel with theabove-indicated clutches and brakes so as to make shift control easy. Ifa one-way clutch is provided in parallel with the second clutch, forexample, the transmission establishes the 1^(st)-speed gear stage onlyby engaging the first clutch. Furthermore, the transmission can shiftfrom the 1^(st)-speed gear stage to the 2^(nd)-speed gear stage only byengaging the first brake. When an engine brake is not needed, a one-wayclutch may be provided in place of the second brake. Here, one-wayclutches function, like brakes, to stop rotation of correspondingrotating members. Other than the above-described arrangements, theautomatic transmission of the invention may be constructed in variousways. For example, a brake and a one-way clutch, which are connected inseries, may be provided in parallel with the first brake.

[0039] Referring to attached figures, the first embodiment of theinvention will hereinafter be described in detail.

First Embodiment

[0040]FIG. 1a schematically shows an automatic transmission 10 of amotor vehicle according to the first embodiment of the invention, andFIG. 1b is an operation table useful for explaining the relationshipbetween engaging elements and gear ratios when a plurality of gearstages are established. The automatic transmission 10 is mounted in thelateral direction in a vehicle, such as a FF vehicle, and includes asub-transmitting portion 14 and a main transmitting portion 20. Thesub-transmitting portion 14 mainly includes a first planetary gear set12 of a double-pinion type, and the main transmitting portion 20 mainlyincludes a second planetary gear set 16 of a single-pinion type and athird planetary gear set 18 of a double-pinion type. The automatictransmission 10 thus constructed transmits rotary power from an inputshaft 22 to an output gear 24 while changing the speed of rotation. Thesub-transmitting portion 14 is the first transmitting portion whereasthe main transmitting portion 20 is the second transmitting portion. Theinput shaft 22, which corresponds to the above-indicated input member,is a turbine shaft of a torque converter which is rotated by a drivingpower source such as an internal combustion engine. The output gear 24,which corresponds to the above-indicated output member, drives orrotates right and left driving wheels via a differential gear unit anddrive shafts. It is to be noted that the automatic transmission 10 isconstructed substantially symmetrically with respect to the center line,and only the upper half of the transmission 10 is illustrated in FIG.1a.

[0041] The first planetary gear set 12 that constitutes thesub-transmitting portion 14 has a sun gear S1, a carrier CA1 and a ringgear R1. The sun gear S1 is coupled to and driven (i.e., rotated) by theinput shaft 22, and the carrier CA1 is fixed integrally to atransmission case 26 and is thus inhibited from rotating, while the ringgear R1, as an intermediate output member, is rotated at a reduced speedas compared with that of the input shaft 22, to output power to the maintransmitting portion 20. Each of the second and third planetary gearsets 16, 18 that constitute the main transmitting portion 20 has a sungear S2, S3, a carrier CA2, CA3 and a ring gear R2, R3. The second andthird planetary gear sets 16, 18 provide four rotating elements RM1-RM4by connecting parts of the gear sets 16, 18 with each other. Morespecifically, the sun gear S2 of the second planetary gear set 16 andthe carrier CA3 of the third planetary gear set 18 are coupled to eachother to provide the first rotating element RM1, and the carrier CA2 ofthe second planetary gear set 16 and the ring gear R3 of the thirdplanetary gear set 18 are coupled to each other to provide the secondrotating element RM2. The ring gear R2 of the second planetary gear set16 provides the third rotating element RM3, and the sun gear S3 of thethird planetary gear set 18 provides the fourth rotating element RM4.

[0042] The first rotating element RM1 (i.e., sun gear S2, carrier CA3)is selectively coupled to the case 26 by a first brake B1 so that itsrotation is stopped, and the second rotating element RM2 (i.e., carrierCA2, ring gear R3) is selectively coupled to the case 26 by a secondbrake B2 so that its rotation is stopped. The fourth rotating elementRM4 (i.e., sun gear S3) is selectively coupled via a first clutch C1 tothe ring gear R1 of the first planetary gear set 12 as the intermediateoutput member, and the first rotating element RM1 (i.e., sun gear S2,carrier CA3) is selectively coupled via a second clutch C2 to the ringgear R1, while the second rotating element RM2 (i.e., carrier CA2, ringgear R3) is selectively coupled to the input shaft 22 via a third clutchC3. The first rotating element RM1 (i.e., sun gear S2, carrier CA3) isselectively coupled to the input shaft 22 via a fourth clutch C4. Thethird rotating element RM3 (i.e., ring gear R2) is coupled integrally tothe output gear 24 so as to output rotary power. Each of the first brakeB1, second brake B2 and the first through fourth clutches C1-C4 is ahydraulically operated friction device of a multiple-disc type, which isfrictionally engaged by means of a hydraulic cylinder. In addition, aone-way clutch F1 is disposed in parallel with the second brake B2,between the second rotating element RM2 (i.e., carrier CA2, ring gearR3) and the case 26. The one-way clutch F1 is adapted to allow thesecond rotating element RM2 to rotate in the same direction as the inputshaft 22, but inhibit the same element RM2 from rotating in the reversedirection.

[0043]FIG. 2 is a nomogram in which straight lines represent the speedsof rotation of the respective rotating elements of the sub-transmittingportion 14 and the main transmitting portion 20. In the nomogram of FIG.2, the lower horizontal line indicates rotation speed “0”, and the upperhorizontal line indicates rotation speed “1.0” which is equal to therotation speed of the input shaft 22. Three vertical lines in thesection of the sub-transmitting portion 14 respectively represent thecarrier CA1, the ring gear R1 and the sun gear S1 as viewed from theleft to the right in FIG. 2. The intervals of these vertical lines aredetermined in accordance with the gear ratio ρ1 (=the number of teeth ofthe sun gear/the number of teeth of the ring gear) of the firstplanetary gear set 12. Four vertical lines in the section of the maintransmitting portion 20 respectively represent the first rotatingelement RM1 (sun gear S2, carrier CA3), the second rotating element RM2(carrier CA2, ring gear R3), the third rotating element RM3 (ring gearR2) and the fourth rotating element RM4 (sun gear S3) as viewed from theleft to the right in FIG. 2. The intervals of these vertical lines aredetermined in accordance with the gear ratio ρ2 of the second planetarygear set 16 and the gear ratio ρ3 of the third planetary gear set 18.

[0044] As is apparent from the nomogram of FIG. 2, when the first clutchC1 and the second brake B2 are engaged, and the fourth rotating elementRM4 is rotated at a reduced speed via the sub-transmitting portion 14while rotation of the second rotating element RM2 is stopped, the thirdrotating element RM3 coupled to the output gear 24 is rotated at a speeddenoted by “1^(st)” in FIG. 2, so that the 1^(st)-speed gear stagehaving the largest gear ratio is established.

[0045] When the first clutch C1 and the first brake B1 are engaged, andthe fourth rotating element RM4 is rotated at a reduced speed via thesub-transmitting portion 14 while rotation of the first rotating elementRM1 is stopped, the third rotating element RM3 is rotated at a speeddenoted by “2^(nd)” in FIG. 2, so that the 2^(nd)-speed gear stagehaving a smaller gear ratio than that of the 1^(st)-speed gear stage isestablished.

[0046] When the first clutch C1 and the second clutch C2 are engaged,and the main transmitting portion 20 is rotated as a unit at a reducedspeed via the sub-transmitting portion 14, the third rotating elementRM3 is rotated at a speed denoted by “3^(rd)” in FIG. 2, which is equalto the rotation speed of the ring gear R1 of the sub-transmittingportion 14, so that the 3^(rd)-speed gear stage having a smaller gearratio than that of the 2^(nd)-speed gear stage is established.

[0047] When the first clutch C1 and the fourth clutch C4 are engaged,and the fourth rotating element RM4 is rotated at a reduced speed viathe sub-transmitting portion 14 while the first rotating element RM1 isrotated as a unit with the input shaft 22, the third rotating elementRM3 is rotated at a speed denoted by “4^(th)” in FIG. 2, so that the4^(th)-speed gear stage having a smaller gear ratio than that of the3^(rd)-speed gear stage is established.

[0048] When the first clutch C1 and the third clutch C3 are engaged, andthe fourth rotating element RM4 is rotated at a reduced speed via thesub-transmitting portion 14 while the second rotating element RM2 isrotated as a unit with the input shaft 22, the third rotating elementRM3 is rotated at a speed denoted by “5^(th)” in FIG. 2, so that the5^(th)-speed gear stage having a smaller gear ratio than that of the4^(th)-speed gear stage is established.

[0049] When the third clutch C3 and the fourth clutch C4 are engaged,and the main transmitting portion 20 is rotated as a unit with the inputshaft 22, the third rotating element RM3 is rotated at a speed denotedby “6^(th)” in FIG. 2, which is equal to the rotation speed of the inputshaft 22, so that the 6^(th)-speed gear stage having a smaller gearratio than that of the 5^(th)-speed gear stage is established.Meanwhile, the gear ratio of the 6^(th)-speed gear stage is 1.

[0050] When the second clutch C2 and the third clutch C3 are engaged,and the first rotating element RM1 is reduced at a reduced speed via thesub-transmitting portion 14 while the second rotating element RM2 isrotated as a unit with the input shaft 22, the third rotating elementRM3 is rotated at a speed denoted by “7^(th)” in FIG. 2, so that the7^(th)-speed gear stage having a smaller gear ratio than that of the6^(th)-speed gear stage is established.

[0051] When the third clutch C3 and the first brake B1 are engaged, andthe second rotating element RM2 is rotated as a unit with the inputshaft 22 while rotation of the first rotating element RM1 is stopped,the third rotating element RM3 is rotated at a speed denoted by “8^(th)”in FIG. 2, so that the 8^(th)-speed gear stage having a smaller gearratio than that of the 7^(th)-speed gear stage is established.

[0052] When the second clutch C2 and the second brake B2 are engaged,the first rotating element RM1 is rotated at a reduced speed via thesub-transmitting portion 14, and rotation of the second rotating elementRM2 is stopped. As a result, the third rotating element RM3 is rotatedin the reverse direction at a speed denoted by “Rev” in FIG. 2, so thata reverse gear stage “Rev” is established. Further, when the fourthclutch C4 and the second brake B2 are engaged, the first rotatingelement RM1 is rotated as a unit with the input shaft 22 and rotation ofthe second rotating element RM2 is stopped. As s result, the thirdrotating element RM3 is rotated in the reverse direction at a higherspeed than that denoted by “Rev” in FIG. 2, so that a second reversegear stage having a small gear ratio than that of the reverse gear ratio“Rev”, namely which is a high-speed reverse gear, is established.

[0053] The operation table of FIG. 1b indicate the relationship betweenthe respective gear stages and the operating states of the clutchesC1-C4 and the brakes B1, B2. In FIG. 1b, “◯” indicates engagement, and“502 ” indicates engagement only at the time of application of an enginebrake. Since the one-way clutch F1 is provided in parallel with thesecond brake B2 for establishing the 1^(st)-speed gear stage, the secondbrake B2 is not necessarily engaged when the vehicle is started (oraccelerated). The transmission gear ratios of the respective gear stagesare suitably determined depending upon the respective gear ratios ρ1, ρ2and ρ3 of the first, second and third planetary gear sets 12, 16 and 18.For example, if ρ1 is equal to 0.485, ρ2 is equal to 0.453, and ρ3 isequal to 0.475, the gear ratios as indicated in FIG. 1b are provided. Asis understood from FIG. 1b, the step value of the gear ratios, namely,the ratio of the gear ratios of the adjacent gear stages is generallyappropriate, and the total width of the gear ratios, namely, the ratioof the largest gear ratio to the smallest gear ratio (=5.04/0.69), is asufficiently large value (which is about 7.32). In addition, the reversegear stage “Rev” has an appropriate gear ratio. Thus, the automatictransmission 10 provides appropriate speed-change characteristics overthe entire range of operation.

[0054] With the automatic transmission 10 of the embodiment, the eightforward speeds (or forward-drive gear stages) are provided by threeplanetary gear sets 12, 16, 18, four clutches C1-C4 and two brakes B1,B2. Thus, the automatic transmission 10 is made light-weight andcompact, and can be more easily installed on the vehicle, as comparedwith the case where four planetary gear sets are used. Furthermore,since shifting from one speed to another speed is effected only bychanging the combination of two of the clutches C1-C4 and the brakes B1,B2, shift control can be easily performed, and shift shocks areadvantageously reduced.

[0055] When the gear ratios ρ1, ρ2 and ρ3 of the three planetary gearsets 12, 16 and 18 are respectively set within a range of about 0.3 to0.6, the automatic transmission 10 is able to provide appropriatespeed-change characteristics over the entire range of operation as shownin FIG. 1b while keeping the size (or diameter) of the planetary gearsets 12, 16, 18 relatively small.

[0056] Next, a modified example of the first embodiment will beexplained. In the following description of the modified example, thesame reference numerals will be used to identify substantially the sameelements or portions as those of the first embodiment.

[0057] The automatic transmission 30 shown in FIG. 3 is modified fromthe transmission 10 so as to be installed on a FR vehicle (so as to beinstalled in the longitudinal direction of the vehicle). In theautomatic transmission 30, the third clutch C3 and the fourth clutch C4are disposed in a side opposite toward the sub-transmitting portion 14,namely in the front side of the vehicle, while the third rotatingelement RM3, namely the ring gear R2 of the second planetary gear set16, is integrally coupled to an output shaft 32, as the above-indicatedoutput member, which drives or rotates drive wheels via a propellershaft and a differential gear unit.

Second Embodiment

[0058]FIG. 4a is a schematic vehicle showing an automatic transmission40 of a motor vehicle according to the second embodiment of theinvention. FIG. 4b is an operation table useful for explaining therelationship between engaging elements and gear ratios when a pluralityof gear stages are established. FIGS. 1a, 1 b, and 5 correspond to FIGS.1a, 1 b, and 2, respectively.

[0059] The automatic transmission 40 is to be installed on in thelongitudinal direction of a vehicle such as a FR vehicle. With theautomatic transmission 40, rotary power is transmitted from an internalcombustion engine as a driving power source to the input shaft 22 via atorque converter 42, and is output from the output shaft 32 to thedriving wheels via the propeller shaft and so on. The main transmittingportion 20 has substantially the same construction as the automatictransmission of the above-described first embodiment, but positions ofthe second planetary gear set 16 and the third planetary gear set 18 areinterchanged. In the sub-transmitting portion 44, the carrier CA1 of thefirst planetary gear set 12 of a double pinion type is coupled to androtated by the input shaft 22, and the sun gear S1 is fixed to the case26 and is thus inhibited from rotating, while the ring gear R1, servingas an intermediate output member, is rotated at a reduced speed ascompared with that of the input shaft 22, to output power to the maintransmitting portion 20 via a selected one of the clutches C1 and C2.

[0060] In this case, too, eight forward gear stages, i.e., the1^(st)-speed gear stage through the 8^(th)-speed gear stage, and onereverse gear stage “Rev” are established according to the operationtable of FIG. 4b that is identical with that of FIG. 1b. Thetransmission gear ratios of the respective gear stages are suitablydetermined depending upon the respective gear ratios ρ1, ρ2 and ρ3 ofthe first, second and third planetary gear sets 12, 16 and 18. Forexample, if ρ1 is equal to 0.500, ρ2 is equal to 0.500, and ρ3 is equalto 0.444, the gear ratios as indicated in FIG. 4b are provided, wherethe step value of the gear ratios is generally appropriate and the totalwidth of the gear ratios (=5.014/0.667) is a sufficiently large value(which is about 7.521). Thus, the automatic transmission 40 of thesecond embodiment operates in substantially the same manner and yieldssubstantially the same effects as that of the first embodiment.

[0061] Besides, FIG. 6 shows an automatic transmission 44 of a motorvehicle as a modified example of the automatic transmission 40 of thesecond embodiment. In the automatic transmission 44, positions of thesecond planetary gear set 16 and the third planetary gear set 18 of themain transmitting portion 20 are interchanged.

Third Embodiment

[0062]FIG. 7a is a schematic view showing an automatic transmission 50of a motor vehicle according to the third embodiment of the invention.FIG. 7b is an operation table useful for explaining the relationshipbetween engaging elements and gear ratios when a plurality of gearstages are established. FIGS. 7a, 7 b, and 8 correspond to FIGS. 1a, 1b, and 2, respectively.

[0063] The automatic transmission 50 is different from the automatictransmission 40 shown in FIG. 5 in respect of the construction of thesub-transmitting portion 52. More specifically, the sub-transmittingportion 52 of the automatic transmission 50 mainly includes the firstplanetary gear set 54 of a single pinion type, in which the ring gear R1is coupled to and rotated by the input shaft 22, and the sun gear S1 isfixed to the case 26 and is thus inhibited from rotating, while thecarrier CA1, serving as an intermediate output member, is rotated at areduced speed as compared with that of the input shaft 22, to outputpower to the main transmitting portion 20 via the clutch C1 and/or theclutch C2.

[0064] With the automatic transmission 50 of the embodiment, like theautomatic transmission 40 shown in FIGS. 4a and 4 b, the maintransmitting portion 20 includes three planetary gear sets 54, 16, 18,four clutches C1-C4 and two brakes B1, B2, but is able to establishseven forward speeds (or forward-drive gear stages) as indicated inFIGS. 7b and 8. More specifically, when the first clutch C1 and thesecond brake B2 are engaged to each other and the fourth rotatingelement RM4 is rotated at a reduced speed via the sub-transmittingportion 52 while rotation of the second rotating element RM2 is stopped,the third rotating element RM3 coupled to the output shaft 32 is rotatedat a speed denoted by “1^(st)” so that the 1^(st)-speed gear stagehaving the largest gear ratio is established.

[0065] When the first clutch C1 and the first brake B1 are engaged toeach other and the fourth rotating element RM4 is rotated at a reducedspeed via the sub-transmitting portion 52 while rotation of the firstrotating element RM1 is stopped, the third rotating element RM3 coupledto the output shaft 32 is rotated at a speed denoted by “2^(nd)”, sothat the 2^(nd)-speed gear stage having a larger gear ratio than that ofthe 1^(st)-speed gear stage is established.

[0066] When the first clutch C1 and the second clutch C2 are engaged toeach other and the main transmitting portion 20 is rotated as a unit ata reduced speed via the sub-transmitting portion 52, the third rotatingelement RM3 coupled to the output shaft 32 is rotated at a speed denotedby “3^(rd)”, which is equal to the rotation speed of the carrier CA1 ofthe sub-transmitting portion 52, so that the 3^(rd)-speed gear stagehaving a larger gear ratio than that of the 2^(nd)-speed gear stage isestablished.

[0067] When the first clutch C1 and the fourth clutch C4 are engaged,and the fourth rotating element RM4 is rotated at a reduced speed viathe sub-transmitting portion 52 while the first rotating element RM1 isrotated as a unit with the input shaft 22, the third rotating elementRM3 is rotated at a speed denoted by “4^(th)”, so that the 4^(th)-speedgear stage having a smaller gear ratio than that of the 3^(rd)-speedgear stage is established.

[0068] When the third clutch C3 and the fourth clutch C4 are engaged,and the main transmitting portion 20 is rotated as a unit with the inputshaft 22, the third rotating element RM3 is rotated at a speed denotedby “5^(th)”, which is equal to the rotation speed of the input shaft 22,so that the 5^(th)-speed gear stage having a smaller gear ratio thanthat of the 4^(th)-speed gear stage is established. Meanwhile, the gearratio of the 5^(th)-speed gear stage is 1.

[0069] When the second clutch C2 and the third clutch C3 are engaged,and the first rotating element RM1 is rotated as at a reduced speed viathe sub-transmitting portion 52, while the second rotating element RM2is rotated as a unit with the input shaft 22, the third rotating elementRM3 is rotated at a speed denoted by “6^(th)”, so that the 6^(th)-speedgear stage having a smaller gear ratio than that of the 5^(th)-speedgear stage is established.

[0070] When the third clutch C3 and the first brake B1 are engaged, andthe second rotating element RM2 is rotated as a unit with the inputshaft 22 while rotation of the first rotating element RM1 is stopped,the third rotating element RM3 is rotated at a speed denoted by“7^(th)”, so that the 7^(th)-speed gear stage having a smaller gearratio than that of the 6^(th)-speed gear stage is established. Also,when the second clutch C2 and the second brake B2 are engaged, the firstrotating element RM1 is rotated at a reduced speed via thesub-transmitting portion 52, and rotation of the second rotating elementRM2 is stopped. As a result, the third rotating element RM3 is rotatedin the reverse direction at a speed denoted by “Rev” in FIG. 2, so thata reverse gear stage “Rev” is established.

[0071] The transmission gear ratios of the respective gear stages aresuitably determined depending upon the respective gear ratios ρ1, ρ2 andρ3 of the first, second and third planetary gear sets 54, 16 and 18. Forexample, if ρ1 is equal to 0.580, ρ2 is equal to 0.550, and ρ3 is equalto 0.392, the gear ratios as indicated in FIG. 7b are provided, wherethe step value of the gear ratios is generally appropriate and the totalwidth of the gear ratios (=4.453/0.645) is a sufficiently large value(which is about 6.902). In addition, the reverse gear stage “Rev” has anappropriate gear ratio. Thus, the automatic transmission 50 providesappropriate speed-change characteristics over the entire range ofoperation.

[0072] With the automatic transmission 50 of the embodiment, the sevenforward speeds (or forward-drive gear stages) are provided by threeplanetary gear sets 54, 16, 18, four clutches C1-C4 and two brakes B1,B2. Thus, the automatic transmission 50 is made light-weight andcompact, and can be more easily installed on the vehicle, as comparedwith the case where four planetary gear sets are used. Furthermore,since shifting from one speed to another speed is effected only bychanging the combination of two of the clutches C1-C4 and the brakes B1,B2, shift control can be easily performed, and shift shocks areadvantageously reduced.

[0073] Further, when the gear ratios ρ1, ρ2 and ρ3 of the threeplanetary gear sets 54, 16 and 18 are respectively set within a range ofabout 0.3 to 0.6, the automatic transmission 50 is able to provideappropriate speed-change characteristics over the entire range ofoperation as shown in FIG. 7b while keeping the size (or diameter) ofthe planetary gear sets 54, 16, 18 relatively small.

[0074] Besides, FIG. 9 shows an automatic transmission 56 of a motorvehicle as a modified example of the automatic transmission 50 of thethird embodiment. In the automatic transmission 56, positions of thesecond planetary gear set 16 and the third planetary gear set 18 of themain transmitting portion 20 are interchanged.

Fourth Embodiment

[0075]FIG. 10a is a schematic view showing an automatic transmission 60of a motor vehicle according to the fourth embodiment of the invention.FIG. 10b is an operation table useful for explaining the relationshipbetween engaging elements and gear ratios when a plurality of gearstages are established. FIGS. 10a, 10 b, and 11 correspond to FIGS. 1a,1 b, and 2, respectively.

[0076] The automatic transmission 60 is different from the automatictransmission 50 shown in FIGS. 7a, 7 b, and FIG. 8 in respect of theconstruction of the sub-transmitting portion 62. More specifically, thesub-transmitting portion 62 mainly includes the first planetary gear set64 of a double pinion type, in which the sun gear S1 is coupled to androtated by the input shaft 22, and the carrier CA1 is fixed to the case26 and is thus inhibited from rotating, while the ring gear R1, servingas an intermediate output member, is rotated at a reduced speed ascompared with that of the input shaft 22, to output power to the maintransmitting portion 20 via the clutch C1 and/or the clutch C2. Namely,the construction of the sub-transmitting portion 62 is identical to thatof the sub-transmitting portion 14 of the automatic transmission shownin FIG. 1

[0077] In this case, too, seven forward gear stages, i.e., the1^(st)-speed gear stage through the 7^(th)-speed gear stage, and onereverse gear stage “Rev” are established according to the operationtable of FIG. 10B that is identical with that of FIG. 7b. Thetransmission gear ratios of the respective gear stages are suitablydetermined depending upon the respective gear ratios ρ1, ρ2 and ρ3 ofthe first, second and third planetary gear sets 64, 16 and 18. Forexample, if ρ1 is equal to 0.630, ρ2 is equal to 0.550, and ρ3 is equalto 0.392, the same gear ratios as indicated in FIG. 7b are provided.Thus, the automatic transmission 60 of the fourth embodiment operates insubstantially the same manner and yields substantially the same effectsas that of the third embodiment.

[0078] Besides, FIG. 12 shows an automatic transmission 66 of a motorvehicle as a modified example of the automatic transmission 60 of thefourth embodiment. In the automatic transmission 66, positions of thesecond planetary gear set 16 and the third planetary gear set 18 of themain transmitting portion 20 are interchanged.

Fifth Embodiment

[0079]FIG. 13a is a schematic view showing an automatic transmission 70of a motor vehicle according to the fifth embodiment of the invention.FIG. 13b is an operation table useful for explaining the relationshipbetween engaging elements and gear ratios when a plurality of gearstages are established. FIGS. 13a, 13 b and 14 correspond to FIGS. 1a, 1b, and 2, respectively.

[0080] The automatic transmission 70 is different from the automatictransmission 60 shown in FIGS. 10a, 10 b and FIG. 11 in respect of theconstruction of the sub-transmitting portion 72. More specifically, hecarrier CA1 of the first planetary gear set 64 is coupled to and rotatedby the input shaft 22, and the sun gear S1 is fixed to the case 26 andis thus inhibited from rotating, while the ring gear R1, serving as anintermediate output member, is rotated at a reduced speed as comparedwith that of the input shaft 22, to output power to the maintransmitting portion 20 via the clutch C1 and/or the clutch C2.

[0081] In this case, too, seven forward gear stages, i.e., the1^(st)-speed gear stage through the 7^(th)-speed gear stage, and onereverse gear stage “Rev” are established according to the operationtable of FIG. 13B that is identical with that of FIG. 7b. Thetransmission gear ratios of the respective gear stages are suitablydetermined depending upon the respective gear ratios ρ, ρ2 and ρ3 of thefirst, second and third planetary gear sets 64, 16 and 18. For example,if ρ1 is equal to 0.370, ρ2 is equal to 0.550, and ρ3 is equal to 0.392,the same gear ratios as indicated in FIG. 10b are obtained. Thus, theautomatic transmission 70 of the fifth embodiment operates insubstantially the same manner and yields substantially the same effectsas that of the forth embodiment.

[0082] Besides, FIG. 15 shows an automatic transmission 74 of a motorvehicle as a modified example of the automatic transmission 70 of thefifth embodiment. In the automatic transmission 74, positions of thesecond planetary gear set 16 and the third planetary gear set 18 of themain transmitting portion 20 are interchanged.

[0083] In each of the automatic transmissions of the first to fifthembodiments describe above, the first planetary gear set is provided inthe first transmitting portion. In place of the first planetary gearset, however, various other deceleration devices or mechanisms may beused such as a biaxial deceleration mechanism including a counter gearor gears.

[0084] Further, the positional relationship between first and secondtransmitting portions and the positional relationship between second andthird planetary gear sets of the second transmitting portion are notparticularly limited to those of the above-described embodiments, butmay be changed as needed. For example, the third planetary gear set maybe disposed between the first planetary gear set and the secondplanetary gear set. The clutches and brakes may also be arranged invarious fashions. For example, the clutches and brakes may be arrangedto be concentrated in one end portion of the automatic transmission.

[0085] In each of the automatic transmissions of the first to fifthembodiments describe above, moreover, the second planetary gear set isof a single pinion type while the third planetary gear set is of adouble pinion type. However, for example, these gear sets may both be ofa single pinion type or of a double pinion type. Also, couplingconstructions of the respective rotating elements of the two planetarygear sets may be modified as needed.

[0086] While the invention has been described with reference toexemplary embodiments thereof, it is to be understood that the inventionis not limited to the exemplary embodiments or constructions. To thecontrary, the invention is intended to cover various modifications andequivalent arrangements. In addition, while the various elements of theexemplary embodiments are shown in various combinations andconfigurations, which are exemplary, other combinations andconfigurations, including more, less or only a single element, are alsowithin the spirit and scope of the invention.

1-10. (Cancelled).
 11. An automatic transmission, comprising: an inputmember; an output member; a first transmitting portion including theinput member that is rotated at reduced speed to output power from anintermediate output member, and a second transmitting portion includinga second planetary gear set and a third planetary gear set each of whichincludes a sun gear, a carrier and a ring gear, at least one of the sungear, the carrier and the ring gear of the second planetary gear setbeing coupled to at least one of the sun gear, the carrier and the ringgear of the third planetary gear set to provide a first rotatingelement, a second rotating element, a third rotating element and afourth rotating element, which are arranged in the order of descriptionfrom one end to the other end in a nomogram in which speeds of rotationof the first, second, third and fourth rotating elements are representedby straight lines, the second transmitting portion further including afirst brake that selectively stops rotation of the first rotatingelement, a second brake that selectively stops rotation of the secondrotating element, a first clutch that selectively couples the fourthrotating element to the intermediate output member, a second clutch thatselectively couples the first rotating element to the intermediateoutput member, a third clutch that selectively couples the secondrotating element to the input member, and a fourth clutch thatselectively couples the first rotating elements to the input member, thethird rotating element being integrally coupled to the output member tooutput rotary power, wherein a first-speed gear stage having the largestgear ratio is established when the first clutch and the second brake areengaged, a second-speed gear stage having a smaller gear ratio than thatof the first-speed gear stage is established when the first clutch andthe first brake are engaged, a third-speed gear stage having a smallergear ratio than that of the second-speed gear stage is established whenthe first clutch and the second clutch are engaged, and a fourth-speedgear stage having a smaller gear ratio than that of the third-speed gearstage is established when the first clutch and the fourth clutch areengaged, a fifth-speed gear stage having a smaller gear ratio than thatof the fourth-speed gear stage is established when the third clutch andthe fourth clutch are engaged, a sixth-speed gear stage having a smallergear ratio than that of the fifth-speed gear stage is established whenthe second clutch and the third clutch are engaged, a seventh-speed gearstage having a smaller gear ratio than that of the sixth-speed gearstage is established when the third clutch and the first brake areengaged.
 12. The automatic transmission according to claim 11, wherein:the first transmitting portion includes a first planetary gear sethaving a sun gear, a carrier, and a ring gear, one of the sun gear, thecarrier, and the ring gear being coupled to and rotated by the inputmember, another being fixed and inhibited from rotating, a remaining oneserving as an intermediate output member and rotating at a reduced speedas compared with that of the input member to output power to the secondtransmitting portion.
 13. The automatic transmission according to claim12, wherein: the third planetary gear set is disposed between the firstplanetary gear set and the second planetary gear set as viewed in anaxial direction of the automatic transmission.
 14. The automatictransmission according to claim 13, wherein: the first planetary gearset is of a double pinion type; and one of the sun gear and the carrieris coupled to the input member, and the other is fixed and inhibitedfrom rotating, while the ring gear serving as the intermediate outputmember is rotated at a reduced speed as compared with that of the inputmember to output power to the second transmitting portion.
 15. Theautomatic transmission according to claim 13, wherein: the firstplanetary gear set is of a single pinion type; and one of the sun gearand the ring gear is coupled to the input member, and the other is fixedand inhibited from rotating, while the carrier serving as theintermediate output member is rotated at a reduced speed as comparedwith that of the input member to output power to the second transmittingportion.
 16. The automatic transmission according to claim 12, wherein:the second planetary gear set is disposed between the first planetarygear set and the third planetary gear set as viewed in an axialdirection of the automatic transmission.
 17. The automatic transmissionaccording to claim 16, wherein: the first planetary gear set is of adouble pinion type; and one of the sun gear and the carrier is coupledto the input member, and the other is fixed and inhibited from rotating,while the ring gear serving as the intermediate output member is rotatedat a reduced speed as compared with that of the input member to outputpower to the second transmitting portion.
 18. The automatic transmissionaccording to claim 16, wherein: the first planetary gear set is of asingle pinion type; and one of the sun gear and the ring gear is coupledto the input member, and the other is fixed and inhibited from rotating,while the carrier serving as the intermediate output member is rotatedat a reduced speed as compared with that of the input member to outputpower to the second transmitting portion.
 19. The automatic transmissionaccording to claim 12, wherein: the second planetary gear set is of asingle pinion type, and the third planetary gear set is of a doublepinion type; and the first rotating element comprises the sun gear ofthe second planetary gear set and the carrier of the third planetarygear set that are coupled to each other, the second rotating elementcomprises the carrier of the second planetary gear set and the ring gearof the third planetary gear set that are coupled to each other, thethird rotating element comprises the ring gear of the second planetarygear set, and the fourth rotating element comprises the sun gear of thethird planetary gear set.
 20. The automatic transmission according toclaim 11, wherein: the second planetary gear set is of a single piniontype, and the third planetary gear set is of a double pinion type; andthe first rotating element comprises the sun gear of the secondplanetary gear set and the carrier of the third planetary gear set thatare coupled to each other, the second rotating element comprises thecarrier of the second planetary gear set and the ring gear of the thirdplanetary gear set that are coupled to each other, the third rotatingelement comprises the ring gear of the second planetary gear set, andthe fourth rotating element comprises the sun gear of the thirdplanetary gear set.